Composite articles comprising an elastomeric base material and reinforcing fibers are known in the art. Reinforcing fibers improve mechanical properties, such as abrasion resistance, tensile strength, compression resistance, and the like in a composite article. Fiber distribution and orientation affect such properties, and controlling fiber orientation is important for providing a composite article having specific mechanical properties.
Known techniques for orienting reinforcing fibers in an elastomeric material are generally methods for orienting fibers in a composite in a direction which is consistent with and parallel to the material flow direction in processing equipment. It is difficult to orient reinforcing fibers in a composite article in a direction which differs from the direction of material flow, and it is especially difficult to orient fibers in a composite in a direction perpendicular to the flow of the material in processing equipment.
One method for orienting fibers in a composite article in a direction which varies from the direction of material flow is disclosed in U.S. Pat. No. 5,156,907 wherein a heated mixture of molding compound (glass) and fibers (carbon) is injected through an elongated injection port into a die. The injection port has a thickness which is purported to be between 30%-70% of the die thickness. The optimum fiber length is 0.5 inches (1.27 cm) for the particular carbon fiber/glass matrix utilized.
U.S. Pat. No. 5,281,380 discloses a fiber reinforced elastic sheet in which staples are oriented in the vertical direction of the sheet. Staple material, such as Nylon 66, is mixed into thermoplastic material and extruded through a molding die. The molding die includes a weir portion which is said to initially orient the fibers in the flow direction. Downstream from the weir portion is a flow passage which has a dimension at least twice that of the weir portion. After passing through the weir portion, the flow direction is changed, thereby changing the fiber orientation with respect to the sheet surface. The sheet so formed can then be further processed for an intended application.
JP 1304924 A (dated Dec. 8, 1989) describes orientation of short fibers in a rubber matrix using an extruder with an expanding die. An elastomer is extruded through a passage running from a cylindrical inlet space to a cylindrical outlet space to produce a cylinder axis body.
BE 842865 (dated Dec. 12, 1976) describes extrusion dies for balancing flow orientation, causing radial divergence to counter longitudinal orientation of fiber, filers, etc.
RD 186061 A (dated Oct. 10, 1979) describes dispersed fibers in a reinforced strip, for example a bead filler, by extruding the strip through a die which orients fibers mainly in a plane perpendicular to the extrusion axis. The fibers are extruded in a thermoplastic or thermosetting polymer.
In PCT/US96/15237, methods and apparatuses are described for orienting short fibers (fibers having a length of 0.1 microns to 103 microns) in a composite article formed by injection molding a molding compound comprising a fiber/elastomeric material blend. The fibers utilized are known as “short fibers” in the art.